Nuclear fuel rods are manufactured from openended zirconium alloy tubular rods. Fissionable pellets are inserted into the rods which are end-plugged. The completed fuel rods are arranged in a skeletal structure containing as many as 264 fuel rods and other core component rods and control rods. This structure is placed into the reactor housing to form its core thereat.
In a nuclear reactor, the nuclear fuel contained within each fuel rod undergoes fission which increases the temperature and pressure within the rods. Any hydrogenous impurities present in the rods typically form hydrides causing the rod to leak radioactive products into the coolant. To minimize internal rod decay and hydriding during reactor operation, the interior of the rods are cleaned during their manufacture by blowing through the fuel rods felt or urethane cleaning plugs. However, during the cleaning process, a cleaning plug or portion thereof may become lodged within the rod. If visual inspection does not locate the cleaning plug before the rod is filled with fissionable pellets and then girth and seal welded, the cleaning plug is retained therein. During reactor operation, the cleaning plug will lead to hydriding causing rod leakage and subsequent contamination of the reactor coolant. Consequently, it is necessary to assure that no obstruction, such as a cleaning plug, is retained within the fuel rod before the fissionable pellets are inserted therein and the fuel rod is welded. Current visual inspection systems have been found inadequate because a cleaning plug or other obstruction can cause a partial obstruction which is difficult to detect.
It is therefore an object of this invention to provide a method and apparatus for sensing obstructions, such as a cleaning plug, in a tubular nuclear fuel rod or the like without using a visual inspection system.
It is still another object of this invention to provide a method and apparatus for sensing obstructions, such as a cleaning plug, in a tubular nuclear fuel rod or the like, which is adapted for repeatable use with many fuel rods.
It is another object of the present invention to provide a method and apparatus for sensing obstructions, such as a cleaning plug, in a tubular nuclear fuel rod or the like, where an audible alarm signal can be generated if an obstruction is present.